Utilization of portable storage devices, e.g., USB memory and the like, is increasing. Although private information of an individual such as a security certificate or the like is stored in the portable storage devices, the information is exposed to other people and frequently lost or stolen in many case due to the portability, and probability of leaking the important data stored therein to outside is also getting increased.
However, many of the portable storage devices are not equipped with a security function for the internal data. Although some of the portable storage devices have the security function, the security level is low, and it is not easy to use since a user should set details of security. Particularly, when the security is set using separate security software, a host computer is heavily loaded, and thus there is a limit in encrypting the data in real-time.
Furthermore, an encryption key value used in the process of encrypting or decrypting a data can be exposed while the encryption key value is read from the host computer.